Pressure responsive piston acuated switch and valve means

ABSTRACT

A pressure responsive mechanism for use in dual hydraulic brake systems of automative vehicles wherein the front and rear brakes of the vehicle are provided with independent hydraulic brake systems actuated by a dual master cylinder, the pressure responsive mechanism being interposed between the dual master cylinder and the front and rear brake actuators and incorporating means actuable when a predetermined pressure differential occurs between the front and rear brake systems to effect a signal and being automatically reset when the pressure differential falls below a predetermined value. The pressure responsive mechanism includes switch actuator means and a pair of pressure responsive members disposed on opposite sides of and normally spaced from said actuator means, but movable into contact with said actuator means upon normal brake operation, and moving said actuator means if brake failure should occur.

United States Patent [191 Kish et al.

[ 1 June 5,1973

[54] PRESSURE RESPONSIVE PISTON ACUATED SWITCH AND VALVE MEANSInventors: George R.. Kish, Owosso; Kenneth FOREIGN PATENTS ORAPPLICATIONS 813,553 5/1959 Great Britain ..200/82 D 75 Primary Examiner-Robert K. Schaefer Swanson, Bannister, both f AssistantExaminer-Robert A. Vanderhye Mich, AttmeyMcKinnon & Groh [73] Assignee:ivlitclllagtlll koss Corporation, Cleve- [57] ABSTRACT an 1o vA pressureresponsive mechanism for use in dual Flledi y 19, 1971 hydraulic brakesystems of automative vehicles [21] APPL No: 164,134 wherein the frontand rear brakes of the vehicle are provided with independent hydraulicbrake systems Related US. Application Data actuated by a dual mastercylinder, the pressure responsive mechanism being interposed between the[62] 52 1 2 2? June 1970 dual master cylinder and the front and rearbrake acv tuators and incorporating means actuable' when a predeterminedpressure differential occursbetween 2% 8 6& the front and rear brakesystems to effect a signal and d 200 153 v being automatically resetwhen the pressure dif- 1 e o are 1 63 ferential falls below apredetermined value. The presl l sure responsive mechanism includesswitch actuator I means and a pair of pressure responsive members [56]References Cited disposed on opposite sides of and normally spacedUNITED STATES PATENTS from said actuator means, but movable into contact1 with said actuator means upon normal brake opera- 3,614,169 10/1971Bueler ..200/82 D X tion, and moving said actuator means if brakefailure 3,480,333 11/1969 Stelzer should occur, 3,394,401 7/1968 Roberts3,637,963 1/1972 Wcllman ..200/82 D 10 Claims, 6 Drawing Figures 1 g TQ- 22 27! J E a; I 24 1 /0 i I /.46 :2! J0 lm/z. f 2;, -,w.fi1mQ// 4 a lIQFEM i "lli\\ srr n l l gk l lgliigli'l\(fi r*sl I] l 545 v1 4a "Q'I'SMH jWW 7 0276 T 1131 M M /5 w m 2/6 m-u. 1 V w a swan a w 52 \l "n\\ w z//0 113% ,i/ W Nae-fill lse l z 12 g &

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PAIENI JUN 5mm v sum 1 0r 2 PRESSURE RESPONSIVE PISTON ACUATED SWITCHAND VALVE MEANS CROSS REFERENCE TO RELATED APPLICATIONS This applicationis a division of the applicants" copending application Ser. No. 47,718,filed June 19, 1970.

' SUMMARY OF THE INVENTION This invention relates to pressure responsivemechanisms and, more particularly, to an improved pressure responsivemechanism particularly adapted for use in dual or split automotivevehicle hydraulic brake systems wherein one set of brake actuators, forexample, the brakeactuators at the front wheels of the vehicle areactuated by a first hydraulic system while another set of brakeactuators, such as the brake actuators at the rear wheels, are actuatedby a second hydraulic system which is hydraulically independent of thefirst hydraulic-system. Thepresent invention is also applicable to othertypes of dual hydraulic brake systems such as dual brake systems whereinthe wheels of the vehicle are each provided with a plurality of brakeactuators, the actuators at each wheel being actuated by independenthydraulic systems. It shouldalso be understood that the presentinvention is applicable to other hydraulic or pneumatic dual or splitSystems.

As is well known in the art, in order to increase the safety factor inautomotive vehicle hydraulic brake systems, many modern automotivevehicles such as automobiles and trucks are equipped with dual hydraulicbrake systems, conventionally known as split systems, wherein hydraulicbrake fluid is delivered from one pressurizable cylinder of a dualmaster cylinder through a first system of brake lines to the brakeactuators or wheel cylinders at the front wheels of the vehicle andhydraulic brake fluid is also delivered from a second pressurizablecylinder of the dual master cylin- 'der through a second system of brakelines to the brake actuators or wheel cylinders at the rear wheels ofthe vehicle, the two separate cylinders of the dual master cylinderbeing simultaneously pressurized upon the application of force by thevehicle operator to a brake pedal effective to actuate the dual mastercylinder. With such a construction, in the event of loss of brakingaction at one set of wheels due to loss of brake fluid or pressure inone half of the split system, actuation of the dual cylinder is stilleffective to apply the brakes at the other set of wheels bypressurization of the other half of the split system.

As also known in the art, during deceleration of an automotive vehicle,a portion of the weight borne by the rear wheels of the vehicle istransferred to the front wheels of the vehicle and as a result of suchweight transfer, the maximum braking effort which the rear wheels arecapable of applying is reduced and the maximum braking effort which thefront wheels are capable of applying is increased. Consequently, it isdesirable to deliver higher brake fluid pressures to the front brakeactuators of the vehicle than to the rear brake actuators of the vehicleduring high rates of deceleration such as are encountered during panicstops so that the skidding tendencies of the rear wheels are reduced,control of the vehicle may be maintained and the stopping distancedecreased. Consequently, various pressure proportioning valves have beenutilized in hydraulic brake the brake pedal if one or the other of thehydraulic systems has failed or is not operating properly. Moreover, ifthe vehicle is equipped with a proportioning valve effective toestablish a fluid pressure differential between the front and rear brakeactuators in the higher ranges of pressure applied by the mastercylinder, and a failure occurs resulting in loss of pressurization ofthe front system while pressurization of the rear brake actuators hasbeen reduced relative to the front brake actuators, it is desirable toimmediately apply the maximummaster cylinder pressure to the rear brakeactuators so that the maximum available braking action of the vehiclemay be obtained under such conditions.

Heretofore, a various --pressure responsive switches have beenutilizedin dual hydraulic brake systems of automotive vehicles, thepressure responsive switches being adapted to complete an electricalcircuit effective to energize a signaling device to apprise the vehicleoperator that a failure has occurred in one or the other of the dualhydraulic brake systems. However, prior pressure responsive switches ofthe indicated character have been subject to the defect that they mustbe replaced or removed from the hycraulic system for resetting purposesafter they have been actuated, and the labor and expense incident toreplacement or manual resetting of such prior devices by an automobilemechanic materially increases the cost of vehicle maintenance. v i Anobject of the present invention is to overcome disadvantages in priorpressure responsivemechanisms of the indicated character and to providean improved pressure responsive mechanism which is particularly adatpedfor use in dual hydraulic brake systems of automotive vehicles whereinthe front and rear brakes are actuated by independent hydraulic brakesystems; which is actuable to effect a signal when a predeterminedpressure differential occurs between the dual hydraulic brake systemsand which is automatically-reset when the pressure differential in suchhydraulic systems is reduced below a predetermined minimum.

Another object of the invention'is to provide an improved pressureresponsive mechanism actuable to effect full pressurization of the rearbrake hydraulic sys tem of an automotive vehicle equipped with pressureproportioning means in the event of loss of pressurizathe event of apredetermined reduction of pressure in Y the other of such systems.

Another object of the invention is to provide an improved pressureresponsive mechanism incorporating improved means for closing a pair ofelectrical contacts when a predetermined pressure differential occurs ina dual hydraulic system of an automotive vehicle and opening suchelectrical contacts when the pressure differential is restored to avalue below a predetermined minimum.

Another object of the invention is to provide an improved pressureresponsive mechanism actuable to effect a signal when a predeterminedpressure differential occurs between two hydraulic systems andsimultaneously control the flow of fluid through one of such systems.

Another object of the invention is to provide an improved pressureresponsive mechanism facilitating the detection of failures in dualhydraulic brake systems of automotive vehicles.

Still another object of the invention is to provide an improved pressureresponsive mechanism that is economical and commercially feasible tomanufacture, assemble and test with mass production labor and methods,durable efficient and reliable in operation.

The above as well as other objects and advantages of the presentinvention will become apparent from the following description, theappended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view of apressure responsive mechanism embodying the present invention, showingthe same in association with schematically illustrated components of anautomotive vehicle hydraulic brake system;

FIG. 1A is an enlarged view of a portion of the structure illustrated inFIG. 1.

FIG. 2 is a graph illustrating the manner in which the pressure curvesat the front and rear brake actuators of an automotive vehicle divergeas the result of pressure proportioning means operating in a dualhydraulic brake system;

FIG. 3 is an enlarged cross-sectional view of a portion of the structureillustrated in FIG. 1, taken on line 33 thereof;

FIG. 4 is a top view of the annular valve embodied in the structureillustrated in FIG. 1, showing the same removed therefrom; and

FIG. 5 is a cross-sectional view of the annular valve illustrated inFIG. 4, taken on the line 5-5 thereof.

DETAILED DESCRIPTION Referring to the drawings, a pressure responsivemechanism, generally designated 10, is illustrated embodying the presentinvention, the pressure responsive mechanism having particular utilityin hydraulic brake systems of automotive vehicles of the typediagrammatically illustrated in FIG. 1, although it will be understoodthat the present invention is applicable to other uses. Hydraulic brakesystems of the type illustrated in FIG. 1 are conventionally known asdual or split brake systems, and in such systems, hydraulic fluid isdelivered from a dual master cylinder 12 actuated by a conventionalbrake pedal 14, a power booster (not shown) being interposed, ifdesired, between the brake pedal 14 and the dual master cylinder 12 toboost the manual effort applied by the driver of the vehicle. Hydraulicfluid is delivered from the outlet 15 of the dual master cylinderthrough a line 16 to the brake actuators or wheel cylinders 18 and 20 ofthe front wheels of the vehicle, and hydraulic fluid is also deliveredfrom the outlet 22 of the dual master cylinder 12 to the brake actuatorsor wheel cylinders 24 and 26 provided at the rear wheels of the vehicle,the pressure responsive mechanism 10 being interposed between the dualmaster cylinder 12 and the brake actuators 19, 20, 24 and 26.

The dual master cylinder 12 and the brake actuators 18, 20, 24 and 26are of conventional construction and operation and their use is so wellknown in the art that a detailed description thereof is not required fora full understanding of the present invention.

In the embodiments of the invention illustrated, the pressure responsivemechanism 10 incorporates a proportioning valve, generally designated28, which may be of the type disclosed and claimed in the co-pendingapplication of George R; Kish and Edward L. Volker, Ser. No. 874,483,filed Nov. 6, 1969 for Proportioning Valve and assigned to the assigneeof the present invention. As shown in FIG. 1, the pressure responsivemechanism 10 is comprised of a body 30 and the proportioning valve 28 isincorporated in the body 30 as a part of the pressure responsivemechanism but it will be understood that the proportioning valve 28 maybe embodied in a separate structure if desired. In the preferredembodiment of the invention illustrated, the body 30 defines a steppedborev 32 which communicates with an inlet port 34 connected by a line 36to the outlet 22 of the dual master cylinder 12 as illustrated,

diagrammatically in FIG. 1, a flare fitting such as 38 being provided atthe inlet port 34 of the body 30 to facilitate connection of thepressure responsive mechanism to the line 36. The body 30 of thepressure responsive mechanism also includes an outlet port 40 connectedto the rear wheel brake actuators 24 and 26 by a line 42 having asuitable T-connection 43 to the rear wheel brake actuators 24 and 26, aninternally flared fitting 44 which will be described hereinafter ingreater detail being provided at the port 40 to facilitate connection ofthe line 42 to the body of the pressure responsive mechanism.

The proportioning valve assembly, generally designated 28, includes apressure responsive member or piston 48 (which is preferably formed ofmetal or other suitable material having sufficient strength to withstandthe forces exerted thereon) and an annular, resilient valve element 50(which is preferably formed of rubber or other suitable resilientmaterial, the pressure responsive member or piston 48 and the annularvalve element 50 being disposed in the stepped bore 32 and being adaptedto control communication between the inlet port 34 and the outlet port40. The stepped bore 32 defined by the body 30 includes a reduceddiameter portion 52 at the inner end thereof which communicates with theoutlet port 40 through a passageway 54 defined by the body 30. Thestepped bore 32 also includes an intermediate portion 56 which is largerin diameter than the portion 52 while the lower end portion 58 of thestepped bore 32 is larger in diameter than the portion 56 andcommunicates with the inlet port 34 through a passageway 60 definedby-the body 30. The lower end portion 58 of the stepped bore is closedby a cap 62 which threadably engages the body 30, an O- ring 64 beinginterposed between the cap 62 and the body 30 to provide a fluid tightseal sealing the threaded connection between the cap 62 and the body 30.The central portion 66 of the cap defines an axially extending bore 68adapted to receive the cylindrical stem portion 70 of the pressureresponsive member 48 for reciprocating movement therein, a conventionalquad-ring seal 72 being provided which is disposed in a groove 74defined by the central portion 66 of the cap, the quadring seal 72providing a double acting fluid tight dynamic seal between the stemportion of the pressure responsive member and the cap. A boot 76 issecured to the end cap 62 by an integral flange 78, the boot surroundingthe lower end portion 80 of the piston stem 70 and functioning toprevent the entrance of foreign material into the bore 68 defined by thecentral portion of the cap.

In addition to the cylindrical stem 70, the pressure responsive member48 includes an integral intermediate portion 82 having opposed flatsides 84 and 86 joined by curvilinear surfaces 88 and 90 which arepreferably formed as arcs of a circle, the intermediate portion 82 inturn being integral with a head portion 92, the upper end of which is ofcastellated form having angularly spaced projections 94 definingangularly spaced fluid passageways 96 therebetween. The head portion 92also includes an annular axially extending lip portion 98 which isgreater in diameter than the stem portion 70 and which projectsdownwardly as viewed in FIG. 1.

The pressure responsive member 48 also includes a radially extendingflange portion 100 having flat sides 102 and 104 preferably disposed inthe planes of the flat sides 84 and 86, respectively, of theintermediate portion 82 of the pressure responsive member and beingjoined by curvilinear surfaces 106 and 108 preferably formed as arcs ofa circle concentric with but greater in diameter than the curvilinearsurfaces 88 and 90 of ithe central portion 82, the radius of curvatureof thef curvilinear portions 106 and 108 being less than the radius ofcurvature of the cylindrical section 56 of the stepped bore 32. i

The annular valve element 50 includes a body 110 defining a centrallydisposed bore 111, the upper end of the body being of castellated formto define angu larly spaced, upwardly extending projections 1 12defining angularly spaced fluid passageways 114 therebetween aroundthevperiphery of the upper sealing surface 115 of the body 110. Theannular valve element 50 also includes a skirt portion 116 whichprojects angularly outwardly and downwardly from the body portion, asviewed in FIG. 1, and engages the internal wall of the body defining theintermediate section 56 of the stepped bore 32, the annular valve 50being disposed in the intermediate portion 56 of the stepped bore sothat the upper ends of the projections 112 bear against the shoulder 118provided on the body portion between the intermediate portion 56 and thereduced diameter portion 52 of the stepped bore. The lower surface 120of the body portion of the annular valve bears against the upper surface122 of the flange portion 100 of the pressure responsive member 48.

As shown in FIG. 1, the pressure responsive member 48 is biased upwardlyby a coil spring 124 the lower end portion of which bears against thecap member 62 while the upper end portion of the spring 124 bearsagainst a spring retainer 126, the spring retainer having an axiallyextending flange portion 128 the upper end of which bears against thelower surface 130 of the flange portion 100 of the pressure responsivemember In the preferred embodiment of the invention illustrated, thebody 30 also defines a stepped bore 132 the .longitudinal axis of whichextends in a direction substantially perpendicular to the longitudinalaxis of the stepped bore 32. The left end portion 133 of the bore 132,as viewed in FIG. 1, communicates with asecond inlet port 134 that isconnected to the outlet 15 of the dual master cylinder 12 by the line16, a suitable flare fitting 136 being provided at the inlet port 134 tofacilitate connection of the line 16 to the body '30. The inlet port 134and the left end portion 133 of the bore 132 also communicate withoutlet passageways 138' and 140 connected to outlet ports 142 and 144 byan outlet passageway 146, the outlet port 142 being connected to thefront wheel brake actuator 18 by a line 148 while the outlet port 144 isconnected to the front wheel brake actuator 20 by a line 150. Suitableflare fittings 152 and 154 are provided at the outlet ports 142 and 144,respectively, to facilitate connection of the lines 148 and to the body30. With such a construction the hydraulic pressure of the fluid flowingthrough the line 16 is applied to the front wheel brake actuators l8 and20, the fluid flowing from the inlet port 134 through the left endportion of the bore 132 to the outlet passageways 138, 140 and 146 andthen to the outlet ports 142 and 144 and the lines 148 and 150,respectively, to the actuators 18 and 20. v

The stepped bore 132 includes an intermediate portion 156 which islarger in diameter than the portion 133 of the stepped bore, theintermediate portion 156 merging with the enlarged right end portion ofthe stepped bore that defines the outlet port 40 previously described.The intermediate portion 156 of the bore 132 communicates with the inletport 34 and with the passageway 60 leading to the chamber 58.

The right end or outlet portion 40 of the bore 132 is closed by thevalve fitting 44 which threadably engages the body 30 as at 158, asuitable seal 160 being-interposed between the body and an end flange162 provided on the fitting 44 to provide a fluid tight seal between thefitting 44 and the body 30.

An elongate actuating member 164 is provided which is mounted forreciprocal movement in the r educed diameter portion 133 of the steppedbore 132. The actuating member 164 includes a central body portion 166and a pair of reduced diameter end portions 168 and 170 which projectaxially outwardly from the opposite ends of the central portion 166. Thecentral portion 166 defines a groove 172 providing ramp surfaces 174 and176 which are adapted to engage a plunger 178 provided on an electricalswitch mechanism, generally designated 180, which will be describedhereinafter in greater detail. The ramp surfaces 174 and 176 are adaptedto engage the adjacent rounded end of the plunger 178 selectively whenthe actuating member moves off center with respect to the plunger.

A pair of pistons 182 and 184 are provided which are disposed in theportion 133 of the stepped bore on'opposite ends of the actuating member164. In the embodiment of theinvention illustrated the pistons 182 and184 are identical in construction and made interchangeable for purposesof economy of manufacture but it will be understood by those skilled inthe art that the pistons need not be identical. In the embodiment of theinvention illustrated each of the pistons 182 and 184 includes a headportion 186, a reduced diameter neck portion 188 and a foot portion 190.The head portions 186 of each of the pistons define an annular groove192 adapted to receive an O-ring seal 194 providing a fluid tight sealbetween the head portions of the pistons and the wall 196 of the body 30defining the portion 133 of the stepped bore 132. The head portions 186of each of the pistons 182 and 184 also define an axially extendingblind bore 198 adapted to receive the reduced diameter end portions 168and 170 of the actuating member 164. The neck portions 188 of each ofthe pistons 182 and 184 define a transversely extending passageway 200and the neck and foot portions of each of the pistons also define anaxially extending counterbore 202 as shown in FIG. 1.

As shown in FIG. 1, under normal conditions and with the brakes in thenon-applied condition, the reduced diameter end portions 168 and 170 ofthe actuating member 164 project partially into the blind bores 198 ofthe pistons 182 and 184 so that the ends of the portions 168 and 170 ofthe actuating member are disposed in spaced relationship with respect tothe end walls 204 of the blind bores 198. Since pistons 182 and 184 arespring biased and normally spaced from actuator portions 168 and 170,they will be moved each time the brakes are applied instead .of onlywhen a failure occurs. This is desirable because it prevents sticking atseals 194 due to non-use when a failure does occur.

A sleeve 210 is provided which encompasses the medial portion of theactuating member 164 including the groove 172, the sleeve 210 beingprovided with an opening 212 through which the end portion of theplunger 178 projects into the groove 172 provided in the actuatingmember. A pair of coil springs 214 and 216 are provided which spacedlysurround the opposite end portions of the actuating member, one end ofthe spring 214 bearing against the head portion of the piston 182 whilethe opposite end of the spring 214 bears against the adjacent end of thesleeve 210. One end of the spring 216 bears against the head portion ofthe piston 184 while the opposite end of the spring 216 bears againstthe adjacent end of the sleeve 210.

The valve fitting 44 includes a head portion 218 which is disposed inthe outlet port 40 defined by the body 30 and which threadably engagesthe body 30 at 158. The valve fitting 44 also includes a reduceddiameter neck portion 220 and a base portion 222. The neck portion 220and the base portion 222 are disposed in the intermediate portion 156 ofthe stepped bore 132 and the base portion 222 defines an annular groove224 adapted to receive an O-ring seal 226 providing a fluid tight sealbetween the base portion and the wall 228 of the body defining theintermediate portion 156 of the stepped bore 132. An outlet passageway230 extends through the fitting 44, the passageway 230 including asection 232 which communicates with the inlet port 34 through thecounterbore 202 and the transverse passageway 200 of the piston 184. Theinner end of the section 232 communicates with an intermediate, reduceddiameter, axially extending section 234 of the outlet passageway 230,the section 234 terminating adjacent a conventional flared seat 236disposed in an in ternally threaded section 238 of the outlet passageway230, the flared seat 236 being adapted to seat against a conventionalexternally threaded flare fitting (not shown) provided on the line 42 ina conventional manner.

Angularly disposed passageways 240 and 242 are provided in the fitting44, the outer ends of the passageways 240 and 242 communicating with theintermediate section 228 of the stepped bore 132 while the inner ends ofthe passageways 240 and 242 communicate with the section 234 of theoutlet passageway 230. With such a construction the passageway 54communicates with the line 42 through the angularly disposed passageways240 and 242 and the intermediate section 234 of the outlet passageway230.

The radially disposed surface 244 at the intersection of the sections232 and 234 of the outlet passageway 230 provides a valve seat for avalve generally desig-' against the seat 244 by a coil spring 264 oneend of which bears against the shoulder 256 while the opposite end ofthe coil spring 264 bears against a snap ring 266 which spacedlysurrounds the leg portion 260 of the valve 246, the peripheral portionsof the snap ring gripping the piston 184. With such a construction,movement of the piston 184 to the left, as veiwed in FIG. 1, causes thesnap ring to engage the foot portion 262 of the valve so as to move theresilient valve element 248 off of the seat 244 so as to opencommunication through the outlet passageway 230 from the inlet port 34to the line 42, the valve element 248 being held off of the seat as longas the piston 184 is displaced to the left a distance greater than thedistance between the foot portion 262 of the valve and the snap ring266.

In the embodiment of the invention illustrated the switch includes abody 270 which threadably engages the body 30 as at'272, a seal 274being disposed between the body 270 and the body 30 so as to provide afluid tight seal therebetween. The body 270 carries an electricallyinsulated conductor 276 which is electrically connected to the vehiclebattery 278 in circuit with a signaling device, such as a lamp 280,which is preferably I disposed on the vehicle dashboard and which, whenenergized, functions to apprise the vehicle operator of a failure in thedual hydraulic brake system. The conductor 276 is also electricallyconnected to a contact 282 carried by an electrical insulator 284disposed in a recess 286 defined by the body 270. The plunger 178includes a flange portion 288 and an axially projecting contact portion290 adapted to make and break with the contact 282, the, contact portion290 of the plunger being biased toward the open position by a spring 292one end of which bears against the flange 288 of the plunger 178 whilethe opposite end of the spring 292 bears against the insulator 284. Theplunger 178 passes through a sleeve 294.preferably formed ofelectrically conducting material such as brass. The lower end of thesleeve 294 projects into the opening 212 provided in the sleeve 210 soas to prevent relative perpendicular movement between the sleeve 210 andthe sleeve 294 while the rounded lower end of the plunger 178, as viewedin FIG. 1, projects beyond the adjacent end of the sleeve 294 and intothe groove 172 of the actuating member 164.

The body 30 is also formed of a metallic electrically conductingmaterial and is electrically grounded as at 300 in a conventional mannerso that when the contacts 282 and 290 are closed, an electrical circuitis completed from battery through the lamp 280, conduc-' tor 276, thecontacts 282 and 290, the plunger 178, sleeve 294 and the body 30 toground so as to energize the lamp 280.

In the operation of the pressure responsive mechanism 10, assuming aninitial condition in which no manual force is being applied to the brakepedal 14, the components of the pressure responsive mechanism 10 'willbe disposed in the positions illustrated in FIG. 1.

The graph of FIG. will be referred to in conjunction with the operationof the proportioning valve 28 to indicate the relationship between thepressures at the outlets 15 and 22 of the master cylinder and thepressure at the outlet passageway 230 leading to the rear wheel brakeactuators 24 and 26 of the vehicle. The origin or point of FIG. 2indicates the condition when no manual force is applied to the brakepedal 14, it being understood that in conventional practice the dualmaster'cylinder 12 will have a residual pressure maintained by aresidual check valve (not shown) when the proportioning valve is used ona vehical equipped with drum brakes at the rear wheels so that the rearwheel brake system of the vehicle is maintained under a slight pressureeven though no manual force is applied to the brake pedal 14 therebypreventing the entrance of air into the rear brake system. For purposesof illustration however the residual brake pressure is indicated as zeroat the origin of the graph of FIG. 2. When the vehicle is equiped withdisc brakes at the rear wheels, a residual check valve is notconventionally utilized.

Upon application of manual force to the brake pedal 14, the pressurefrom the outlets 15 and 22 will follow the curve A indicated by thesolid lines while the pressure from the outlet passageway 230 willfollow the solid line (curve A) from the origin 0 to the point C andthereafter will follow the dashed curve B so that'a fluid pressuredifferential is established between the front and rear brake actuatorsin the higher ranges of pressure applied by the master cylinder, thepressure differential being increased at a linear rate as the mastercylinder pressure increases in the higher range. As increased manualforce is applied to the brake pedal 14, the pressure from the outlets land 22 will continue to follow the curve A indicated in solid linebeyond the point C so that the pressure at the outlet of the mastercylinder is applied to the front wheel actuating cylinders 18 and 20through the line 16 but the pressure from the outlet 22 of the mastercylinder is modulated by the proportioning valve 28 and come quently thepressure applied to the rear wheel brake actuators 24 and 26 follows thedashed line B. With equal fluid pressures in the lines 16 and 36,communication to front wheel actuators 18 and 20 is effected in themanner previously described while communication to the rear wheelcylinders 24 and 26 is effected from the outlet 22 of the mastercylinder through the line 36; the inlet port 34; the passageway 60; theportion 58 of the stepped bore 32; the passageway defined between thecontrol portion 82 of the pressure responsive member 48-and the wall ofthe central bore 111 of the annular valve member 50; the reduceddiameter portion 52 of the stepped bore 32; the passageways 96 and 54;and the passageways 240 and 242 to the outlet passageway 230 of theproportioning valve from which the fluid flows through the line 42 tothe rear wheel actuating cylinders 24 and 26. At this stage ofoperation, the

upper ends of the projections 94 on the head portion 92 of the pressureresponsive member remain in engagement with the shoulder at the upperend of the stepped bore 32 due to the biasing action of the spring 124,and the rib 98 remains substantially in the position illustrated in FIG.1 and out of contact with the upper sealing surface. 115 of the annularvalve 50.'As the pressure increases in the stepped bore 32, the fluidpressure acting on the pressure responsive member 48, the effective areaof which at this stage of operation is determined by the diameter of thestem portion 70, tends to move the pressure responsive member downwardlyagainst the biasing action of the spring 124. The spring 124 iscalibrated so that the rib 98 of the pressure responsive member does notengage the sealing surface 115 of the annular valve 50 until the desiredpressure indicated by the point C on the curve A is reached. At suchtime, the rib 98 contactsthe'sealing surface 115 of the annular valve50, thereby closing communication between the intermediate portion 56 ofthe stepped bore 32 and the reduced diameter portion 52 thereof throughthe bore 111 of the annular valve between the intermediate portion 100of the pressure responsive member and the internal wall of the annular.

valve defining the bore 111. Thus the fluid path previously describedfrom the inlet port 34 to the outlet passageway 230 remains open untilthe fluid pressure delivered from the outlet port 22 of the mastercylinder to the stepped bore 32 reaches a predetermined value.

When such value is reached, the annular lip 98 closes against the uppersealing surface 115 of the annular valve, the degree of pressure atwhich this'occurs being dependent upon the force exerted by the spring124 on the pressure responsive member as compared with the effectivearea of the pressure responsive member as determined by thecross-sectional diameter of the stem 3 portion of the pressureresponsive member dynamically sealed in th bore 68 Thus during the lowerranges of applied master cylinder pressure, the pressure actingdownwardly on the effective area of the pressure responsive memberproduces a downward force which is insufficient to overcome the force ofthe spring 124 ex'- erted upwardly against the flange of the pressureresponsive member.

After the lip 98 closes against the upper sealing surface of the annularvalve, and the fluid pressure at the inlet port 34 is further increasedby the master cylinder due to increased manual effort applied by thevehicle driver to the brake pedal 14, the increased fluid pressure willact agianst the pressure responsive member in a direction tending tounseat the annular rib 98 from the sealing surface 115 of the annularvalve 50, the effective area of the pressure responsive member at thistime being determined by the effective diameter of the annular rib 98sealing against the surface 1 15 of the annular valve minus the area ofthe stem 70. The pressure acting against such effective area produces aforce acting on the pressure responsive member tending to assist thespring 124 to unseat the annular rib 98 of the pressure responsivemember from the sealing surface 1 15 of the annular valve 50 so that aportion of the increased pressure is delivered to the outlet passageway230. Such increased fluid pressure, of course, tends to act downwardlyupon the pressure responsive member 48 to produce a force, determined bythe crosssectional area of the stem portion 70, opposing the biasingaction of the spring 124. This tends to reclose the annular lip 98against the upper sealing surface 115 of the annular valve. The annularlip 98 of the pressure responsive member 48 thus opens and closesagainst the sealing surface 115 of the annular valve thereby modulatingthe pressure at the outlet passageway 230 so that the pressure at theoutlet passageway 230 increases at a lower rate than the pressureapplied by the master cylinder with the result that the pressure appliedto the rear brake actuating cylinders 24 and 26 follows the dashed linecurve B from the point C as the master cylinder pressure increases inthe higher range. Accordingly, the fluid pressure existing at the frontbrake cylinders 18 and 20 will be greater than the fluid pressure at therear brake actuating cylinders 24 and 26 when the brakes are appliedwith a force greater than that necessary to move the annular lip 98 ofthe pressure responsive member against the sealing surface 115 of theannular valve in opposition to the spring 124.

Upon a decrease in manual force applied to the brake pedal 14, thepressure in the sections 56 and 58 of the stepped bore tending to movethe pressure responsive member upwardly is reduced because of theincreased volume then provided in the master cylinder. When thedecreasing pressure in the outlet side, acting on its appropriateeffective area, can not support the load imposed by the spring 124, thelip portion 98 moves up wardly away from the sealing surface 115 andreopens the passageway through the bore 111 of the annular valve therebyrelieving the pressure at the rear brake actuators 24 and 26 andequalizing the pressures on opposite sides of the annular valve 50. Asthe pressure at the inlet port 34 is further reduced due to the increasein volume in the master cylinder upon the lowering of the manual forceapplied thereto, the pressure responsive member 48 will be movedupwardly by the spring 124 to reopen the passageway through the bore 111of the annular valve as previously described so that the pressureapplied to the front and rear brakes is equalized and the components ofthe proportioning valve 28 return to the positions illustrated in FIG.1.

As previously mentioned upon application of manual force to the brakepedal 14, the fluid pressure from the outlets 15 and 22 of the mastercylinder 12 follows the curve A indicated by the solid line in FIG. 2and such equal fluid pressures will be applied to the head portions 186of the pistons 182 and 184 through the inlet ports 134 and 34,respectively. As equal fluid pressures are applied to the head portionsof the pistons 182 and 184, the pistons 182 and 184 both move toward theactuating member 164 against the biasing action of the springs 214 and216, respectively, until the ends of the reduced diameter portions 168and 170 of the actuating member bottom on the end wall 204 of the blindbore 198 defined by each piston. Since the fluid pressures applied bythe master cylinder to the inlet ports 134 and 34 are equal, and sincethe effective areas of the head portions of the pistons 182 and 184 areequal, the forces applied by the piston 182 to the actuating member 164are counterbalanced by the forces applied to the actuating member by thepiston 184 and the actuating member remains in the position illustratedin FIG. 1. The valve 246 also remains closed against the seat 244 sincethe distance between the end of the portion 170 of the actuating memberand the end wall 204 of the blind bore 198 defined by the piston 184 isless than the distance between the foot portion 262 of the valve 246 andthe snap ring 266, the snap ring 266 thus remaining out of contact withthe foot portion 262.

Under such conditions the fluid pressure from the outlet 22 of themaster cylinder applied to the rear brake actuators is controlled by theproportioning valve 28 in the manner previously described while thefluid pressure from the outlet 15 of the master cylinder is applied tothe front brake actuators l8 and 20 in the manner previously described.q

Assuming that a failure occurs in the rear wheel hydraulic system, asfor example because of a'break or rupture in the line 36, resulting in aloss or reduction of pressure at the inlet port 34, upon application ofmanual force to the brake pedal 14, the pressure at the 1 move theactuating member 164 to the right, as viewed in FIG. 1. When theactuating member 164 moves to the right, the ramp or cam surface 174engages the adjacent rounded end of the plunger 178 and moves theplunger 178 upwardly as viewed in FIG. 1 and onto the peripheral surfaceof the central portion 166 of the actuating member against the biasingaction of the spring 292. The contact portion 290 of the plunger 178closes against the contact 282 when the plunger 178 moves upwardly onthe ramp surface 174 to complete the electrical circuit through the lamp280 in the manner previously described. When manual force is releasedfrom the pedal 14, the piston 182 will move back to the positionillustrated in FIG. 1 due to the reduction in fluid pressure at theinlet port 134 and the force applied to the piston 182 by the spring214. However the actuating member 164 and the plunger 178 will remaindisplaced and the contacts 282 and 290 will remain in the closedcondition. Consequently the lamp 280 will remain energized as long asthe failure in the rear brake system exists.

It will be understood, of course, that the front hydraulic system willcontinue to function when manual force is applied to the brake pedal 14since the front and rear brake systems are hydraulically independent.

Assuming that the previously described failure of the rear brake systemis then repaired, when manual force is applied to the brake pedal 14after such repair, equal fluid pressures will be applied to the headportions of the pistons 182 and 184. However, since the actuating member164 was displaced toward the piston 184 when the hydraulic failureoccurred, the piston 184'will engage the end of the reduced diameterportion of the actuating member before the piston 182 engages the end ofthe reduced diameter portion 168 of the actuating member and theactuating member will be moved by the piston 184 to the left, as viewedin FIG. 1, thereby enabling the plunger 178 to move back into the groove172 due to the biasing action of the spring 292 thus opening thecontacts 282 and 290 to open the circuit through the lamp 280 andextinguish the lamp.

Assuming now that a hydraulic failure occurs in the front wheelhydraulic system, as for example because of a break or rupture in theline 16 resulting in a loss or reduction of fluid pressure at the inletport 134,

upon application of manual force to the brake pedal 14, the pressure atthe inlet 34 will be substantially greater than the pressure at theinlet port 134 with the result that the fluid pressure applied to thehead of the piston 182 will be substantially less than the fluidpressure applied to the head of the piston 184. Under such conditions,when the piston 184 engages the adjacent end of the reduced diameterportion 170 of the actuating member 164, the piston 184 will overcomethe force exerted by the piston 182 and move the actuating member 164 tothe left, as viewed in FIG. 1. When the actuating member 164 moves tothe left, the ramp or cam surface 176 engages the adjacent rounded endof the plunger 178 and moves the plunger 178 upwardly onto theperipheral surface of the central portion 166 of the actuating memberagainst the biasing action of the spring 292 so that the contact portion290 closes against the contact 282 to complete the electrical circuitthrough the lamp 280 in the manner previously described. When the manualforce is released from the pedal 14, the piston 184 will move back tothe right to the position illustrated in FIG. 1 due to the force appliedby the spring 216 but the actuating member will remain displaced to theleft and the plunger 178 will remain displaced upwardly so that thecontacts 282 and 290 remain in the closed condition. The lamp 280 thusremains energized as long as the failure in the front brake systemexists.

When a failure in the front brake system exists, it is desirable tobypass the proportioning valve means 28 so that the maximum availablehydraulic pressure is applied to the rear wheel brake actuators 24 and26 at all times and even in the higher ranges of pressure applied by themaster cylinder. When a failure in the front brake system exists, themovement of the piston 184 to the left to displace the actuating member164 to the left, as viewed in FIG. 1, causes the snap ring 266 to engagethe foot portion 262 of the valve 246. As the piston 184 continues tomove the left, the valve 246 is unseated from the seat 244 therebyopening the entire outlet passageway 230 so that the fluid pressure atthe inlet port 34 is applied through the outlet passageway 230 to theline 42 thereby bypassing the proportioning valve means 28.

When manual force is released from the brake pedal 14, the piston 184moves back to the right due to the biasing action of the spring 216. Atthe same time the valve 246 closes against the seat 244 due to thebiasing action of the spring 264.

Assuming that the previously described failure in the front hydraulicsystem is then repaired, when manual force is applied to the brake pedal14 after repair of the front system, equal fluid pressures will beapplied to the head portions of the pistons 182 and 184. However sincethe actuating member 164 was displaced toward the piston 182 when thehydraulic failure occurred in the front brake system, the piston 182will engage the end of the reduced diameter portion 168 of the actuatingmember before the piston 184 engages the end of the reduced diameterportion 170 of the actuating member with the result that the actuatingmember will be moved to the right, as viewed in FIG. 1, thereby enablingthe plunger 178 to move back into the groove 172 thus opening thecontacts 282 and 290 to open the circuit through the lamp 280 andextinguish the lamp.

Important advantages of the above described construction reside in thefact that the pressure responsive mechanism is actuatable whenever aloss of pressure occurs in either the front or the rear hydraulic brakesystems to effect a signal apprising the vehicle operator of suchfailure and that the pressure responsive mechanism is automaticallyreset ,upon the first application of fluid pressure thereto after thefailed portion of the system has been repaired. Moreover the pressureresponsive mechanism is actuatable to disable brake proportioning meansin the event of loss of pressure in the front brake system whilepressurization of the rear brake system relative to the front brakesystem has been reduced by the brake proportioning means therebyrestoring full pressurization of the rear brake system.

While a preferred embodiment of the invention has been illustrated anddescribed, it will be understood that various changes and modificationsmay be made without departing from the spirit of the invention.

What is Claimed is:

1. In a pressure responsive mechanism, the combination including a bodydefining a bore, said body having a pair of spaced fluid inletpassageways and a pair of fluid outlet passageways each communicatingwith said bore, an actuating member mounted for longitudinal movement insaid bore intermediate said fluid inlet passageways, a pair of pressureresponsive members disposed in said bore at opposite ends of saidactuating member, each of said pressure responsive members having anabutment surface thereon normally spaced from and movable intoengagement with the adjacent end portion of said actuating member uponan increase in pressure in the adjacent one of said pair of inletpassageways, said actuating member being movable from a first to asecond position by one of said pressure responsive members in responseto a differential in pressure in said inlet passageways, said actuatingmember being movable by the other of said pressure responsive membersfrom said second position to said first position in response to equalpositive pressures in said inlet passageways, valve means carried bysaid body intermediate one of said inlet passageways and one of saidoutlet passageways and controlling the flow of fluid between said oneinlet passageway and said one outlet passageway, a valve seat in saidbody, means biasing said valve means toward said valve seat, and meansoperable in response to movement of said actuating member from a firstto a second position for moving said valve means away from said seat andoperable in response to movement of said actuating member from saidsecond position to said first position to effect movement of said valvemeans toward said seat.

2. The combination as set forth in claim 1 including resilient meansbiasing said abutment surface on each of said pressure responsivemembers away from said adjacent end portion of said actuating member.

3. The combination as set forth in claim 1 including electrical switchmeans carried by said body, and means actuatable in response to movementof said actuating member for opening and closing said switch means.

4. The combination as set forth in claim 1 wherein each of said pressureresponsive members is in the form of a piston mounted for reciprocalmovement in said bore.

5. A pressure responsive mechanism for use in hydraulic brake systems ofautomotive vehicles and adapted to be interposed between a mastercylinder and wheel brake actuators of the vehicle, said pressureresponsive member including a body defining a bore, said body having apair of fluid inlet passageways and a pair of fluid outlet passagewayseach communicating with said bore, said inlet passageways being adaptedto be connected to said master cylinder, said outlet passageways beingadapted to be connected to said wheel brake actuators, an actuatingmember mounted for longitudinal movement in said bore intermediate saidinlet passageways, a pair of pressure responsive members disposed insaid bore at opposite ends of said actuating member, each of saidpressure responsive members having an abutment surface thereon normallyspaced from and movable into engagement with the adjacent end portion ofsaid actuating member upon an increase in pressure in the adjacent oneof said pair of inlet passageways, said actuating member being movablefrom a first to a second position by one of said pressure responsivemembers in response to a differential in pressure in said inletpassageways, said actuating member being movable by the other of saidpressure responsive members from said second position to said firstposition in response to equal positive pressures in said inletpassageways, resilient means biasing each of said abutment surfaces onsaid pressure responsive members away from said adjacent end portion ofsaid actuating member, electrical switch means carried by said body,means operable in response to movement of said actuating member foropening and closing said switch means, a valve member carried by saidbody intermediate one of said inlet passageways and one of said outletpassageways, and means including lost motion means connecting said valvemember to one of said pressure responsive members and operable uponmovement of said actuating member from a first position to a secondposition for opening said valve member and operable in response tomovement of said actuating member from said second position to saidfirst position to close said valve member.

6. The combination as setforth in claim 5 wherein each of said pressureresponsive members is in the form of a piston mounted for reciprocalmovement in said bore.

7. The combination as set forth in claim 5 including a sleeve disposedin said bore and encompassing a portion of said actuating member, meansmaintaining said sleeve in a fixed position relative to said body, saidresilient means bearing against said sleeve and each of said pressureresponsive members.

8. The combination as set forth in claim 5, said actu- I ating memberhaving a pair of spaced cam surfaces thereon adapted to bear againstsaid means for opening and closing said switch means.

9. The combination as set forth in claim 5, said means for opening andclosing said switch means including a plunger projecting into said bore,said actuating member defining a groove adapted to receive said plunger,and resilient means biasing said plunger towards said actuating member.t

10. The combination as set forth in claim 9 including resilient meansbiasing said valve toward the closed position.

1. In a pressure responsive mechanism, the combination including a bodydefining a bore, said body having a pair of spaced fluid inletpassageways and a pair of fluid outlet passageways each communicatingwith said bore, an actuating member mounted for longiTudinal movement insaid bore intermediate said fluid inlet passageways, a pair of pressureresponsive members disposed in said bore at opposite ends of saidactuating member, each of said pressure responsive members having anabutment surface thereon normally spaced from and movable intoengagement with the adjacent end portion of said actuating member uponan increase in pressure in the adjacent one of said pair of inletpassageways, said actuating member being movable from a first to asecond position by one of said pressure responsive members in responseto a differential in pressure in said inlet passageways, said actuatingmember being movable by the other of said pressure responsive membersfrom said second position to said first position in response to equalpositive pressures in said inlet passageways, valve means carried bysaid body intermediate one of said inlet passageways and one of saidoutlet passageways and controlling the flow of fluid between said oneinlet passageway and said one outlet passageway, a valve seat in saidbody, means biasing said valve means toward said valve seat, and meansoperable in response to movement of said actuating member from a firstto a second position for moving said valve means away from said seat andoperable in response to movement of said actuating member from saidsecond position to said first position to effect movement of said valvemeans toward said seat.
 2. The combination as set forth in claim 1including resilient means biasing said abutment surface on each of saidpressure responsive members away from said adjacent end portion of saidactuating member.
 3. The combination as set forth in claim 1 includingelectrical switch means carried by said body, and means actuatable inresponse to movement of said actuating member for opening and closingsaid switch means.
 4. The combination as set forth in claim 1 whereineach of said pressure responsive members is in the form of a pistonmounted for reciprocal movement in said bore.
 5. A pressure responsivemechanism for use in hydraulic brake systems of automotive vehicles andadapted to be interposed between a master cylinder and wheel brakeactuators of the vehicle, said pressure responsive member including abody defining a bore, said body having a pair of fluid inlet passagewaysand a pair of fluid outlet passageways each communicating with saidbore, said inlet passageways being adapted to be connected to saidmaster cylinder, said outlet passageways being adapted to be connectedto said wheel brake actuators, an actuating member mounted forlongitudinal movement in said bore intermediate said inlet passageways,a pair of pressure responsive members disposed in said bore at oppositeends of said actuating member, each of said pressure responsive membershaving an abutment surface thereon normally spaced from and movable intoengagement with the adjacent end portion of said actuating member uponan increase in pressure in the adjacent one of said pair of inletpassageways, said actuating member being movable from a first to asecond position by one of said pressure responsive members in responseto a differential in pressure in said inlet passageways, said actuatingmember being movable by the other of said pressure responsive membersfrom said second position to said first position in response to equalpositive pressures in said inlet passageways, resilient means biasingeach of said abutment surfaces on said pressure responsive members awayfrom said adjacent end portion of said actuating member, electricalswitch means carried by said body, means operable in response tomovement of said actuating member for opening and closing said switchmeans, a valve member carried by said body intermediate one of saidinlet passageways and one of said outlet passageways, and meansincluding lost motion means connecting said valve member to one of saidpressure responsive members and operable upon movement of said actuatingmember from a first position to a second position for opening said valvemember and operable in response to movement of said actuating memberfrom said second position to said first position to close said valvemember.
 6. The combination as set forth in claim 5 wherein each of saidpressure responsive members is in the form of a piston mounted forreciprocal movement in said bore.
 7. The combination as set forth inclaim 5 including a sleeve disposed in said bore and encompassing aportion of said actuating member, means maintaining said sleeve in afixed position relative to said body, said resilient means bearingagainst said sleeve and each of said pressure responsive members.
 8. Thecombination as set forth in claim 5, said actuating member having a pairof spaced cam surfaces thereon adapted to bear against said means foropening and closing said switch means.
 9. The combination as set forthin claim 5, said means for opening and closing said switch meansincluding a plunger projecting into said bore, said actuating memberdefining a groove adapted to receive said plunger, and resilient meansbiasing said plunger towards said actuating member.
 10. The combinationas set forth in claim 9 including resilient means biasing said valvetoward the closed position.